Manufacture of tire treads



'fpatented June 3Q, i925.

assi-,305'

arras.

GEORGE F. FISHER, 0F BOSELLE, NEW JERSEY, ASSIGNOB T0 MORGAN & WBGET,

CQBPRATIGH 0F MICHIGAN.

MANUFACTUBE 0F TIRE TREADS.

\ Application ed February 3, 1922. Serial No. 533,764.

To all whom t may concern.'

Be it known thatI, GEORGE F.- FISHER, a citizen of the United States,residing in Roselle, county of Union, State of New Jersey, have inventedcertain new and useful Improvements in the Manufacture of Tire Treads,of which the following is a full, clear, and exact description.

This invention relates to the manufacture of tires and in particular theproduction of tread stocks therefor.

. In the manufacture of pneumatic casings, it is largely the practice tocalender vulcanizable rubber composition for the treads, first, iuto asheet of substantially uniform thickness, and then, into a strip of acrosssection more or less trapeziform. This is accomplished by passingthe rubber between a pair of parallel cylindrical rolls which form itinto a sheet that is carried around `to the bight of a second pair ofcooperating rolls, one of which is engraved to produce the cross-sectiondesiredin the tread stock. In this old practice, the calendered sheet ofuniform thickness made in the first pass is wider and thinner than thefinished tread stock and consequently, at the. final pass,4

. i. e., the bight between the engraved roll and its co-operating plainroll, the rubber composition is compelled to iiow from its oppositesides towards the center. This direction of iiow is substantially' atright angles to the application of pressure by the calender rolls andfrequently results in an imperfect product, fissures or scales beingformed at the tread center and necessitating discard and re-calenderingof the material. And especially, do these imperfections occuli on thestarting up of a calender, sometimes necessitating a lengthy run beforethe tread stocks are produced enough uniform in cross-section anddensity to pass requirementsand then not being as near perfect asdesired.

I have discovered that tread stocks may be produced more uniform incross-section and density, and without substantial delay onstarting up acalender, by forming them in successive stages. First, I bring thecomposition roughly to the cross-section desired and subsequently,compress or thin the strip and bring it to the final desiredcrosssection. That is to say, I gather the rubber in such mass, shapeand thickness as to permit in the final shaping, a compressing andcompacting of the rubber, insuring the elimination of scales, fissures,or cracks, the movement of the rubber in this final pass, if anything,being from the center-towards theopposite sides of the stripcontrariwise to the old practice. y

An embodiment of the invention is illustrated in the accompanyingdrawings in which:-

Fig. 1 represents diagrammatically in sideelevation a suitable andconvenient arrangement of vcalender rolls,

Fig. 2 is a rear elevation thereof, show ino the first and intermediatepasses,

IFig. 3 is a plan view showing the final pass,

Fig. 4 is a cross-section of a finished tread,

superimposed dotted lines showing its crosssection at the first andintermediate stages.

In the drawings, I have illustrated dia` grammatically a preferredformof calender for carrying on the invention. The rolls of the calenderare indicated at l, 2, 3 and `4, the first three being stackedvertically,

andthe last or fourth roll being arran e'd horizontally to one side ofthe roll 3,'Qor convenience in changing over tomake a` tread stock of aslightly different size or shape. But the relative location or dis-Adisposition of the rolls is widely variable.

Rolls 2 and 4 are preferably engraved as shown at 5 and 6, respectively.uides are employed as .desired and needed to control the width of theplasticv strip, these beiner shown conventiona ly at 8 and 9. vWith thelast roll 4 of the seriesto which the finally formed strip tends tocling" co-operates a knife 10 which trims the margins or aprons of thestock and renders the strip uniform in width. The treadlstock is usuallydelivered lto a conveyor or endless belt 11 being carried away thereby4to a cutting station for y severance at the approximate lengthtoencircle a plied up carcass. "l y According to my inventioh, the stripof tread stock 12, which is continuously formed from a bank 13 ofvulcanizable rubber composition maintainedl between the bight of therolls 1 and 2, is subjected to compression in the final pass between thebight of rolls 3 and 4, and preferably, but not necessarily, by apreceding compression in the intermediate pass between rolls 2 `and 3.In other words, the gaps 14 and 15 between the rolls` 1 and 2 and therolls 2 and 3, respec- 4All) tively, are both preferably greater thanthe gap 16 between the rolls 3 and 4i; ind erably, the gap 15 is lessthan. the gap le', i. e., 'the strip is preferably, hut not necessarily,compressed and thinned in the interu vmediate pass 15 as Well as in thepass 16.

The engravings' and 6 on rolls 2 and 4 are preferably similar, if not:identical7 in which case the successive thinning ci the tread stool;may be obtained by suitably justing the rolls of the calender. But, theengravings 5 and G mey be varied in depth to accomplish this seme end.And While the engraving 5 is preferably similar oridentical Withtheengraving 6, it to he noted that this is not essential. for the roll2 maybe engraved in any suitable manner t0 initially :forniA 'thevulcanizable rnhber composition'into a strip Whose area in cross sectionisgrester than inally desired, and also thicker, at least at its center.n

In the drawings I have illustrated tlie preferred construction in Whichthe engraving 5 is slightly deeper than the engraving 6 and also inwhich the rolls l land 2 are lshown spaced farther apart than the rolls2 and '3, these latter being also spaced farther apart than the rolls 8and 4l in t. e final pass. In Fig. 4, the cross-section of the strip asit is delivered. from theirst pass isindicated at 6, its cross-sectionas it emerges from the second pass between the rolls 2 and 3 isindicated at. And the cross-section of the strip as it is 'completed isindicated in solid lines at 8 iii-Fig. d.

As presently comprehended, the essential principle of the invention isto malte the. rubber composition into a strip slightly A thicker thandesired, afterwards compressing and compactingthe strip to reduce itsthickness andvcompelthe rubber, if anything, to .flow in oppositedirections from the enter towards the sides of the strip in this wafissures scales, or like ini )ei i tions, vare positively eliminatedfrom product. Uhviously, the advantages of invention may he realizedwith other forms e of engraving on the rol-l 2 than that shown,

the ultimate limit being' 'an engraving? of rectangularcross-section'for initially forro ing the rubber into e; strip oflgreater thiclrf ness and area in c erosssection than thenished strip oftread stoel; desired. l prem iter, however, to closely approximate theshape of the outer face of the iinished strip of tread stock in thefirst pass, and to initially make. it thicker than finally required, atleast its center; to then compress and thin the strip somewhat; and tofinally further compress and thin the strip. That is to say, lpreferably so initially' form the strip to subsequently permit`successive compressing ond thinning thereof.

it will7 therefore, he understood that the invention coi'nprehends other:forms of procedure and apparatus than that specifically disclosed,reference being made to 'the claims for an understanding of the scope ofhe invention,

Haring thus described my invention, what ,l clarin and desire to protectby Letters latent is;

l. llhst nietl'i'od of continuously forming; vnlcanizahle rubbercomposition into tread stock which consists in, first forming thecomposition into a-stripv having a greater total area in cross-sectionand also a greater thickness the center than the product sought, andsubsequently compressing the strip, and shaping; it to the desiredforni.

That method of continuously calendering rubber composition to form astrip of fend stock: ,vvhicli consists in, forming; the composition intoa strip of apprexiniately the desired cross-section, and subsequentlycompressing and thinning the stripto the exact crosssecinion desired.

e. That method 'of continuously calendering rnliher composition to fornia strip of tread stock which consists in, forming 'the composition intoa strip of approximately the desired cross-section, and subsequentlyreducing the tl'iiclmess ot the cross-section of' the strip.

4i. A tread calender having, at least two pairs of cooperating rolls,one roll at least'oii e h pair heing engraved., and the engraved rollsdefining' passes of diierent 'thickness tor permitting; successivecompression of a strip of `riihloer composition v)seing ycalende'red.

Signed et New York, county of uNew* York,

und Strate of New Yorlf, vthis" 31st day ofl January, 1922.

` GERGE F. FISHER.

